Xbox and PlayStation. The "problem" is that you want to game on your PC, not that there isn't another viable option.
But yeah, the overall point still stands. If you have a particular game that you don't feel like you can substitute and it's not available on a platform that you'd like to switch to, you're probably not switching to that platform.
I've also seen enough people that are quite skilled with a controller that they perform better than the average keyboard/mouse player, that I think we'll see less people worry about cross-modal play.
I love having the option to game with an Xbox One controller on my PC, and I love that keyboard/mouse preferring players sometimes have that option on the Xbox. Let everyone play what they find fun.
I've been playing a bunch of Sea of Thieves lately, and it's almost surprising there isn't a controversy about cross-platform/cross-modal play, and yet it is open PvP. I don't feel like it matters if I'm using keyboard/mouse or controller, much less if an opposing player is, and that's a weird sort of magic. (It matters more if the opposing players are jerks that don't follow the Pirate Code.) Props to Rare for pulling that off, and maybe that will be increasingly a thing. (The Gears of War cross-platform/cross-modal playlists have gotten good reviews as well, from what I've heard, though I've not specifically tried them.)